1. Technical Field
A light-emitting diode (LED) device and manufacturing methods thereof are provided, and more particularly to a LED device having a transparent conductive oxide (TCO) stack structure and manufacturing methods thereof.
2. Description of the Related Art
The light-emitting diodes (LEDs) of the solid-state lighting elements have the characteristics of low power consumption, low heat generation, long operational life, shockproof, small volume, quick response and good opto-electrical property like emitting stable wavelength and so on, so the LEDs have been widely used in household appliances, indicator light of instruments, optics and photonics products, etc. As the optics and photonics technology develops, the solid-state lighting elements have great progress in increasing the light efficiency, operation life and the brightness. LEDs become the main stream of the lighting devices in the near future.
FIG. 1 shows a cross-sectional view of conventional light-emitting diode device 100. The conventional light-emitting diode device includes a substrate 101, an n-type semiconductor layer 102 epitaxially grown on the substrate 101, an active layer 103, a p-type semiconductor layer 104, a front side electrode 105, and a back side electrode 106 wherein the front side electrode 105 is disposed on the light extraction side of the light-emitting diode device 100 and the back side electrode 106 is formed on the side of the substrate 101 where no epitaxial structure formed on. The driving current R1 is driven from the front side electrode 105 to the p-type semiconductor layer 104, and through the active layer 103 having a double heterostructure or a multi-quantum well structure to emit light. Generally speaking, in order to improve the light efficiency of the light-emitting diode device 100, the current from the front side electrode 105 needs to be spread to the edge of the light-emitting diode device 100 effectively to make the active layer 103 emit light uniformly.
Because of the high contact resistance between the semiconductor layer and the metal electrode of the light-emitting diode device 100, the current R1 cannot spread to the active layer 103 effectively. The current R1 normally flows with the shortest pathway passing through the active layer 103 to the back side electrode 106 and the current crowding effect is therefore occurred. It restrains the lighting area in a portion of the active layer 103 below the front side electrode 105, and greatly influences the light efficiency of the active layer 103.
A known art to resolve the issue is to form a current blocking layer of native conductive oxide by thermal annealing the transparent electrode, or to form a thin film of p-type metal oxide like LixNi1−xO or a p-type nitride like ZrAlN between the outer layer of the p-type epitaxial stack and the transparent electrode of the light-emitting diode to combine with the transparent electrode so the current from the transparent electrode to the light-emitting diode spreads uniformly and the light efficiency of the active layer 103 is increased.
Nevertheless, the native conductive oxide or the hybrid transparent electrode of the p-type metal oxide like LixNi1−xO or the p-type nitride like ZrAlN have the issue of the high contact resistance with the stack structure of the light-emitting diode. In order to lower the contact resistance, small band gap semiconductor materials are needed to form the stack structure. The flexibility to choose material is therefore limited, and the light efficiency of the light-emitting diode is indirectly influenced because of the high operation voltage.
Therefore, a light-emitting diode having low contact resistance, efficient current spreading and better light efficiency with simpler processes is needed.